Multiple-speed interface

ABSTRACT

The present invention provides a security module having a communication interface being capable of operating according to any from a selection from a plurality of predetermined operation modes or communication protocols. The security module further comprises a voltage detector to detect the voltage on the module&#39;s power supply connection. Depending on the value of the detected voltage or to which of a plurality of predetermined voltage ranges the detected voltage may be categorized, the security module is made to function according to one from the plurality of predetermined communication protocols. According to an embodiment of the present invention the plurality of communication protocols require that the security module operate at a plurality of different frequencies

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to. U.S.provisional patent application No. 61/364,854, filed Jul. 16, 2010, andEuropean patent application no. EP10173155.2, filed Aug. 18, 2010, thecontents of which are hereby incorporated by reference herein in theirentireties.

INTRODUCTION

The present invention relates to the domain of conditional access todata, in particular to data of the audio/video type intended, amongothers, for Pay-TV. More specifically, it concerns a security modulecomprising means to process an audio/video signal.

The present invention also relates to a method for processing anencrypted audio/video signal using a security module comprising means toprocess an audio/video signal.

STATE OF THE ART

As it is well known, in order to control access to encrypted audio/videodata allowing the visualization of a Pay-TV event, such as a film, asports event or a game in particular, several data streams are broadcastas part of an encrypted audio/video signal to a plurality ofreceiver/decoders each comprising a descrambler and a security module.In particular, these data streams are on one hand the file of the eventin the form of encrypted audio/video content and on the other hand, astream of control messages known as Entitlement Control Messages, or ECMmessages, allowing the encrypted audio/video content to be decrypted.The audio/video content is encrypted by control words, which areregularly renewed. The ECM messages can be formed in two different ways.According to a first method, the control words are encrypted by a key,known as a transmission key, which generally pertains to thetransmission system between a management centre and the security moduleassociated with the receiver/decoder. The control word is obtained bydecrypting the ECMs by means of the transmission key.

According to a second method, the ECM stream does not directly containthe encrypted control words, but rather contains information allowingfor the determination of the control words. This determination of thecontrol words can be carried out by different operations, in particularby a decryption which may lead directly to the control word, but canalso lead to data which contains the control word, which must then beextracted from that data. In particular, the data can contain thecontrol word as well as a value, associated with the content to bebroadcast, and in particular the access conditions to this content.Another operation allowing the determination of the control word canuse, for example, a one-way hashing function of this data in particular.

In the majority of present-day conditional access systems, the encryptedaudio/video signal is captured by a receiver. The various data streams.comprised in the signal are extracted and the encrypted audio/videocontent is sent to a descrambler for descrambling/decryption. The ECMmessages are sent to a security module where they are decrypted in orderto extract the control words. The control words are transmitted to thedescrambler. Rather than transmitting the control words to thedescrambler in clear, the control words may be sent to the descramblerin encrypted format using a key common to the security module and to thedescrambler. The descrambler contains a descrambling module responsiblefor the decryption of the data stream with the aid of the control words.

During the decryption of a control message ECM, it is also verified, inthe security module, that the right to access the content in question ispresent. This right can be managed by authorisation messages EMM(Entitlement Management Message) that load this right into the securitymodule.

The encryption key for the control messages may itself be transmitted inauthorisation messages EMM, in order to allow access to the controlwords.

The method described above, where the security module passes the controlwords to the descrambler, has a drawback in that it may be possible fora third party to intercept the control words as they are passed from thesecurity module to the descrambler. Furthermore, it is not necessarilyconsidered that the descrambler is a secure element. This may not be abig problem in the case of a broadcast programme where control words arefrequently changed, but in the case where encrypted data is storedrather than broadcast, the notion of duration of the validity of thecontrol words disappears as it is associated with the encrypted data.

In order to solve this problem, a possible solution is to decrypt thecontent directly in the security module. In this way keys and controlwords do not exit the card, because they are used directly inside thecard to process the encrypted content.

At present, a large number of the security modules used in conditionalaccess systems and in particular in conditional access systems relatedto Pay-TV are smart cards. Generally, such smart cards comply with theinternationally accepted industry standard ISO 7816, managed jointly bythe ISO (International Organisation for Standardisation) and the IEC(International Electrotechnical Commission). The ISO 7816 Standardincludes specifications pertaining to the physical disposition ofcontacts used to interface with the smart card and specificationspertaining to the electrical characteristics and operatingcharacteristics of the smart card.

As it is well known, the cards conforming to this standard compriseeight contacts accessible from the exterior by means Of elements whichform an electrical junction with the contacts of the card when thelatter is inserted into a reader. Six of the eight contacts have afunction well defined by the ISO 7816 Standard. In particular, a contactVDD is responsible for providing the power supply to the card's chip, acontact GND provides the grounding of this chip, a contact RST allowsresetting, a contact VPP provides the supply of the chip in programmingvoltage, a contact CLK allows the input of a clock signal and a contactI/O allows the input/output of data. This leaves two contacts which arenot reserved for any particular function according to the ISO 7816Standard. These contacts are referred to as being reserved for futureuse (RFU).

These cards are particularly adapted to a Pay-TV system since they allowthe security required for this type of application to be provided.However, they suffer from a defect. They do not allow significant dataprocessing speeds. Thus, when such cards are used to decrypt controlmessages ECM in order to extract the control words, their processingcapacity is sufficient. However, the processing capability of thesecards is not sufficient for decrypting the large data streams typicallyrequired for audio/video content.

State of the art smart cards may comply with another internationallyaccepted industry standard known as ISO 14443, Which applies tocontactless smart cards, where communication is made through RFtransmission between a reader and a smart card placed sufficiently closeto the reader. Transfer rates using this standard are again insufficientfor decrypting the large data streams typically required for audio/videocontent.

At present there are cards capable of operating in two different modesaccording to two different communications protocols, in particular a,first mode complying with the ISO 7816 Standard and a second mode usinga high speed serial communication protocol such as the USB protocol forexample (Universal Serial Bus). The USB protocol allows for sufficientlyfast rates to provide the processing capacity required for theaccomplishment of the decryption of audio/video content. Otherproprietary communications protocols similarly exist which equally allowfor sufficiently fast rates to provide the processing capacity requiredfor the accomplishment of the decryption of audio/video content. Thistype of proprietary communication protocol may equally be preferred asthe second mode of operation.

In the smart cards conforming to the ISO 7816 Standard, two contacts ofthe eight existing contacts are not reserved for any precise function,and therefore can be used according to particular requirements of anapplication. According to the USB Standard, the data is transmitted bytwo wires, D+ and D−, with two other wires being provided to providepower. Certain existing smart cards thus use the two free contacts of acard complying with the ISO 7816 Standard to ensure the transfer of thedata according to the USB Standard.

For a conventional application, in the ISO 7816 smart cards, the clockfrequency used is generally lower than 5 MHz. The clock signal isgenerated in an external device then transmitted to the card via thecontact CLK of the chip.

In a system using the USB protocol for audio/video signal processing,the clock frequency must not only be very accurate, but it must berelatively high. Generally, the clock frequency in USB mode is 30 MHzand the data transfer rates are 1.5 Mb/s (low speed) or 12 Mb/s (fullspeed) according to the USB 1 Standard and 480 Mb/s (high speed)according to the USB 2.0 Standard. The high frequency and high precisionthus required in the USB mode necessitate the use of a precisionoscillator such as a quartz oscillator, which needs to be integratedonto the USB module itself. When the USB module takes the form of asmart card, constraints related to volume of production and productionyield in particular must be respected. This makes the manufacturing ofthe cards relatively complex and expensive.

Moreover, in a system capable of operating In ISO 7816 mode and in USBmode, it is necessary to manage very different frequencies in the mostflexible possible way.

The document EP 1 457 922 describes a smart card that works in ISO 7816mode and in USB mode, which is capable of switching automatically intothe required mode. This automatic switching is carried out by means ofthe detection of a voltage on the contact D+ or D− of the chip. If avoltage is present on one of these contacts, it is considered that thesmart card operates in USB mode. If no voltage is present on one ofthese contacts, the card operates in ISO 7816 mode.

This mechanism for detecting the mode of operation implies that it isfirst necessary, to generate a voltage or to suppress the voltage on thecontacts D+ and D− in USB mode in order to indicate to the card thatthere is a mode change. The required data can only be transmitted whenthe mode change has been taken into account such a constraint impliesthat this embodiment is not adapted to an application in which the modechanges frequently, in particular when there are frequent changes fromISO 7816 mode for the processing of control messages ECM to USB mode forthe processing of the audio/video stream. According to a particularembodiment of this invention, the detection of the USB mode is carriedout by imposing a logical 1 on the contact CLK. It is clear that in thiscase, the contact is no longer available.

In European Patent Application publication number EP 1 862 947 A1 asecurity module capable of switching between a plurality of differentcommunication protocols based on a detected clock frequency isdescribed.

In European Patent Application Publication number EP 1 833 006 A2 auniversal integrated circuit card (UICC) is described, which can detecta power supply voltage upon power-on. The detected value is attributedto one from a plurality of predetermined categories and the category isused to set the UICC into either a MMC or a USB communication protocol.This is done on a one-time basis at power-on.

The 7816 Standard has evolved to include various so-called classes. Forexample ISO 7816 Class A and ISO 7816 Class B exist for SIM cards, whichmay be considered to be a variant of a smart card. Class A covers SIMcards operating with a supply voltage of 5V and Class B. covers SIMcards operating with a supply voltage of 3V. Class A and Class B can beconsidered to be the same communications protocol but with differentclasses, with both classes operating at different voltages. The datarates of the two, classes are of the same order of frequency. In thepresent invention, these different classes are considered to bedifferent operation modes.

The present invention proposes to solve the problems perceived in theprior art by providing a security module capable of operating in onefrom a plurality of different operation modes in order to processaudio/video data streams according to either a first communicationprotocol, or a second communication protocol of higher speed than thefirst communication protocol. This security module is furthermorecapable of switching automatically from one mode of operation to anotherin a frequent and fast manner thereby being able to process data streamsaccording to any of the different operation modes as and when required.

Furthermore, the present invention removes the constraints related tothe integration of an oscillator onto a smart card. It is thus possibleto produce a relatively cheap card while providing greater flexibilityof use.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a security module for processing anaudio/video data stream, said security module having a communicationinterface being capable of operating according to any one from aplurality of predetermined operation modes. The security modulecomprises a voltage detector to measure the voltage on the module'spower supply connection. The measured voltage is categorised into onefrom a plurality of predetermined voltage ranges and depending on thevoltage range to which the measured voltage pertains, the securitymodule is made to function according to one of the pluralitypredetermined operation modes.

It is a further aim of the present invention to provide a method forprocessing an audio/video signal using: a security module comprisingmeans for processing an audio/video signal, an interface having aplurality of contacts including a power supply contact and a voltagedetector configured to measure a voltage on the power supply contact,said method comprising the following steps:

-   -   applying a power supply to the power supply contact,    -   measuring the voltage on the power supply contact,    -   determining a category to which the measured voltage pertains,        said category being one from a plurality of predefined        categories,    -   selecting, on a frequent basis, an operation mode from a        plurality of predetermined operation modes, said selection        depending on the predetermined category, said operation mode        including any communication protocol from a plurality of        different communication protocols or any class from a plurality        of classes of a communication protocol,    -   operating the security module according to the selected        operation mode.

The security module may function with an external clock. The externalclock may be multiplied in the module or divided in the module in orderfor different frequencies to be made available according to which of theplurality of operation modes is selected. Moreover, the detection of theoperation mode (communication protocol) is carried out automaticallywithout it being necessary to use a dedicated pin of the interface tosignal a mode change.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood thanks to the detaileddescription which follows and the accompanying drawings, which are givenas non-limiting examples of embodiments of the invention, namely:

FIG. 1 showing a schematic representation of the security moduleconfigured according to a first embodiment of the present invention;

FIG. 2 showing a schematic representation of the security moduleconfigured according to another embodiment of the present invention;

FIG. 3 showing a schematic representation of the security moduleconfigured according to a further embodiment of the present invention.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 3, the security module (SM), according toan embodiment of the present invention, essentially comprises aninterface (IF) whose pin-out complies with the ISO 7816 Standard, aprocessor (CP) and a voltage detector (VD). The processor (CP) includeshardware to take care of the security functions such as the decryptionof ECMs and EMMs and furthermore includes hardware to take care of thedecryption of the audio/video content. The output of the processor (CP)is sent for processing to an external a video processing unit (notshown).

The security module also cooperates with a clock signal generator (CG)which is external to the security module (SM) and may be placed forexample in a card reader used for interfacing with the security module(SM). According to an embodiment of a conditional access system for usein the Pay-TV domain, in which an embodiment of the present inventionmay be deployed, the clock signal generator (CG) is placed in a decoder(DEC). The decoder (DEC) includes the smart card reader into which thesecurity module (SM) is introduced when the assembly is in operation.

According to the ISO 7816 Standard, an interface complying with theStandard notably comprises eight contacts, numbered from 1 to 8 in theFigs. The contact having reference 1 (VDD) is the contact though which apower supply is provided to a circuit to which contact is to be made viathe interface (IF). In the context of the present invention the circuitreferred to here is the smart card or security module. Contact 2 (RST)allows for the resetting of the circuit. Contact 3 (CLK) allows for aclock signal to be input to the circuit. Contact 5 (GND) provides thegrounding of the circuit. Contact 6 (VPP) provides a programming voltageto the circuit. Contact 7 (I/O) allows data to be input to the circuitor output from the circuit. Contacts 4 and 8 are reserved for future useand can be considered to be unused when the circuit is operating in amode compliant with the ISO 7816 communication protocol.

As discussed previously, the circuit is adapted to be able to operateeither in a first mode according to a communication protocol defined bythe ISO 7816 Standard or in a second mode according to a communicationprotocol defined by a second standard whose frequency Of operation issignificantly higher than the frequency of operation of the first mode.Examples of such standards to which the second mode of operationcomplies are the USB. Protocol or the LVDS protocol (Low VoltageDifferential Signaling) or even a proprietary communication protocol. Byway of example, typical frequencies of operation of an ISO 7816 typeinterface is of the order of 5 MHZ whereas the frequency of operation ofa USB type interface is around 30 MHz. According to an embodiment of thepresent invention illustrated in FIG. 1, the clock signal generator (CG)generates signals at a sufficiently high frequency to allow the securitymodule to operate in the mode requiring the higher of the two operatingfrequencies.

In order to ensure the precision necessary for reliable operation of thecircuit in the operation mode requiring the higher operating frequency,the clock signal is generated externally to the security module andtransmitted to the security module via the Contact 3 (CLK) of the ISO7816 type interface. In this way there is no conflict between therequirements to mass produce reliable smart cards and the requirement toproduce a highly accurate clock generator.

In order for the circuit to be able to function at the lower of the twooperating frequencies, i.e. when it is operating in the mode compliantwith the ISO 7816 Standard, the security module further comprises afrequency divider (DIV). As mentioned, this frequency is generally inthe range of 3 to 5 MHz. As it is well known, the frequency divider(DIV) can be realised by means of a counter configured to allow afrequency at the input of the divider to be divided by any whole value,or by means of successive stages of frequency dividers dividing thefrequency by 2, thus allowing the input frequency to be divided bypowers of 2. The frequency divider (DIV) can also be arranged to dividethe frequency of the signal at its input in order to make it compatiblewith the higher frequency mode if the frequency of the clock signalgenerated by the clock signal generator is too high for this mode.

The output of the frequency divider (DIV) is connected, via amultiplexer (MX), to Contact 3 (CLK) of the ISO 7816 type interface (IF)in order to provide the circuit with the required clock signal. Asindicated in the Figure, the multiplexer (MX) allows for the output ofthe clock signal generator (CG) to go either directly to the chip, orindirectly, that is to say after passing through the frequency divider(DIV), according to the generated frequency and to the requiredfrequency. It is also possible to use a frequency divider capable ofcarrying out different divisions according to necessity. According to apractical example, the generated frequency could be divided by 12 inorder to allow the circuit to operate in ISO 7816 mode and by 2 to allowthe circuit to operate in a higher frequency mode such as USB mode forexample or some other proprietary higher frequency communicationprotocol.

The security module according to the invention also includes a voltagedetector (VD) arranged to determine the value of the power supply (VDD)used or at least to distinguish a range to which the power supplyvoltage (VDD) belongs according to a predefined set of voltage ranges.According to one embodiment of the present invention three voltageranges are predefined and the voltage detector is capable ofdistinguishing the detected supply voltage (VDD) as belonging to one ofthe three ranges, namely 2.25V-2.75V (LV), 3V-3.6V (MV) or 4.5V-5.5V(HV). Ideally, the three voltage ranges are separated, so that there isno risk of confusion possible between them. According to the embodimentof the present invention, when the circuit is operating in a modecompatible with the ISO 7816 Class A protocol, the power supply will bewithin the highest of the three voltage ranges (HV). Similarly, when thecircuit is operating in a mode compatible with the ISO 7816 Class Bprotocol, the power supply will be within the mid voltage range (MV).When the circuit is operating in a mode compatible with a secondprotocol, having a higher frequency than the ISO 7816 protocol, thepower supply will be within the lowest of the three voltage ranges (LV).The voltage detector can therefore be used to determine the mode ofoperation of the circuit. According to the determined mode of operationof the circuit, the multiplexer (MX) is controlled in such a way as toswitch the appropriate clock signal to the processor (CP).

FIG. 2 shows an embodiment in which the security module of the presentinvention includes a frequency multiplier (MLT) in place of the divider(DIV) of FIG. 1. In this case, instead of using a clock signal generator(CG) that provides a frequency compatible with the operating moderequiring the highest frequency, the generator provides a signal havingthe lowest frequency. This signal can be sent directly to the processorin the case of operating according to the ISO 7816 Standard or can besent to the frequency multiplier. The latter then multiplies thefrequency by a value that makes it compatible with operating in USB modeor in LVDS mode or some other proprietary mode.

In the examples mentioned in the present application, it is indicatedthat the frequency in USB mode is 30 MHz. According to the frequency ofthe clock generator and the characteristics of the multiplier, thefrequency with which the contact CLK of the chip is provided can bedifferent to 30 MHz. Such a different frequency could be used since thedecoder'and the smart card both use the same frequency.

FIG. 3 shows a practical embodiment that is a combination of theembodiments of FIGS. 1 and 2. The security module simultaneouslyincludes a frequency divider (DIV) and multiplier (MLT).

This security module presents the advantage that It can be usedindifferently with an apparatus generating a clock frequency compatiblewith the ISO 7816 protocol or with an apparatus generating a clockfrequency compatible with a protocol using a higher frequency than theISO 7816 protocol. When the generated frequency corresponds to moderequiring the higher frequency, the invention device uses the frequencydivider to generate the clock frequency compatible with ISO 7816 mode.When the generated clock frequency corresponds to ISO 7816 mode, thedevice uses the frequency multiplier to generate a high frequencycorresponding to the mode which is compatible with higher operatingfrequencies.

It is also possible to make provision for the signals generated by theclock signal generator to have an intermediate frequency between thefrequency used in ISO 7816 mode and that corresponding to USB mode, forexample 15 MHz. In this case, when the device operates in ISO 7816 mode,the signals of the clock signal generator are transmitted to thefrequency divider before being sent to the card. On the contrary, whenthe device operates in USB mode, the signals of the generator are sentto the frequency multiplier before being sent to the card.

According to a variant, the smart card can support different serialcommunication modes such as for example USB and LVDS. The clock signalcan be generated at a frequency required by the communication moderequiring the lowest frequency, i.e. the ISO 7816 mode. In this case, afirst multiplication stage is used to generate a frequency that iscompatible with the intermediate mode, i.e. the USB mode in our example.A second multiplication stage is further used to generate a higherfrequency that is compatible with the mode requiring the highestfrequency, i.e. the LVDS mode.

It is also possible to generate an intermediate frequency and to use afrequency divider to generate a lower frequency and a frequencymultiplier to generate a higher frequency. Similarly, it is possible togenerate a frequency at least as high as the frequency required for themode requiring the highest frequency and to use two dividers to generatelower frequencies.

When the security device has determined in which operating mode it mustwork, it carries out the required operations in a conventional way. Assoon as the clock frequency has changed, the operating mode also changesand the processing of the information is adapted consequently.

In the device according to the invention, there is no particularmanagement of the operating mode of the processor. It is only necessaryto act on changes to the power supply voltage to the power supplycontact of the security module (and thereby acting on the clockfrequency seen by the security module) after the initial detection andmode selection on power up so that changes in the operating mode areimmediately or rapidly detected and the new operating mode isimmediately or rapidly selected. In this way the detection and thereforethe mode switching can be done on a continuous basis while the securitymodule is operating. Detection on a “continuous basis” includesgenerally detecting on a frequent basis, as described hereafter, duringthe operation of the security module. In embodiments for use in a Pay TVapplication and targeted towards switching the mode of operationrelative to the speed capability of an interface, “on a frequent basis”can mean at intervals compatible with a possible switching of operationfrom one mode to another, such as when switching between reception ofcontent from one operator or channel to reception of content fromanother operator or channel for example. It will be understood by theman of ordinary skill in the art that detection of a change in the powersupply voltage and switching to the corresponding new mode of operationshould be performed quickly so that the switching delay is tolerable toa user and more preferably should be performed so that the switchingdelay is not noticeable to the user. The frequency could then bedescribed in terms of an event driven phenomenon such as changingbetween channels for example. In other embodiments of the presentinvention the voltage detection could be executed on a periodic orpolled basis such as every two seconds or every quarter of a second forexample. This presents the advantage that it is possible to change theoperating mode very frequently, which is necessary in particular in anapplication such as Pay-TV in which the change between the processing ofthe data stream requiring operating in USB, LVDS or other higherfrequency modes and processing the control messages requiring operatingin ISO 7816 mode is frequent and must be fast. In other words, uponpower on of the device or at some predetermined time following startup,as part of a bootstrap process for example, the voltage on the powersupply pin is detected and depending on the category to which thatmeasured voltage belongs the device is made to function according to oneof the predetermined operating modes. During the functioning of thedevice, if the supply voltage moves and it detected as belonging to adifferent category, then the device is caused to switch to another ofthe predetermined operating modes. This process continues whereby anytime the supply voltage changes to be in another category the device isswitched to function according to another operation mode.

The present invention has been described with reference to an embodimentin which the security device takes the form of a smart card. It ishowever also possible for this device to take another form, for examplethe form of a key or of any object.

According to a particular case, it is possible to foresee that one ofthe operating modes, for example the USB mode, is inactive by defaultand that it is necessary to send a particular command to activate thismode.

According to an embodiment of the present invention, using the samephysical connections as discussed above, communication between a hostdevice and a security module according to one of a plurality ofdifferent communication protocols involving substantially differentclocking frequencies is facilitated. According to this embodiment, anegotiation between the host device and the security module is carriedout. Indeed, whenever the smartcard reader starts up or whenever thesmartcard is inserted into the reader of the host device, the twomentioned parties communicate their respective capabilities with eachother via a predefined protocol. Using the data relative to thecapabilities, it is a simple task for a processor in the host device ora processor on the smartcard to determine the best set of workingconditions which will be acceptable to both parties. The resulting bestconditions would result in a communication session being set up betweenboth parties, which could range anywhere from a low-speed legacy ISO7816 protocol to a very high speed protocol. This process is known asnegotiation. The power supply voltage imposed by the card reader willthen be chosen as a result of this negotiation in order to set the powersupply to the appropriate range for the negotiated communicationfrequency.

According to this embodiment of the present invention, the negotiationbetween the two parties results in the card reader determining a voltagelevel to be used for the power supply pad, thereby forcing the protocolto one of the predetermined protocols based on the power supply voltagedetected by the smartcard.

Another solution to the problem of having a host device automaticallyadjusting itself to operate according to a communication protocol oroperating mode involves the use of a separate pad or pads other than theeight pads on a standard ISO 7816 interface. According to this solution,the smartcard features two physically separate pads—one forlow-bandwidth communication and one for high-bandwidth communication.The first of these two pads could be one of the already existingcommunication pads from the standard. ISO 7816 interface for example.This first pad would be used for low-bandwidth communication. The secondpad would be used for high-bandwidth communication and would bepositioned close to the chip but at a position which would allow a cardreader to detect that it is an extra pad, distinct from the first pad.When the smartcard reader starts up or when the smartcard is insertedinto an active reader, the reader detects the positions of the secondpad relative to the first one i.e. the standard one. According to apredefined protocol, the position of the second extra pad relative tothe position of the first pad gives a code which correlates to the bitrate or clock rate capabilities of the module on the card. In this waythe reader can be informed as to the best data rate it can use incommunicating with the module and switch to that rate. In general, thesecond pad should be very close to the smartcard chip and could even beplaced on the opposite side of the card for example.

According to another embodiment of the present invention with the extrapad as described above, the negotiation is achieved through thedetection of the position of the second pad by the card reader. Theresult of this negotiation indicates to the reader that it should setthe power supply voltage pad to one of the pre-defined voltage ranges,thereby setting the reader into one of the predefined communicationprotocols so that the communication between the card and the reader cancontinue at the required bit-rate.

1. A security module comprising: a processor for processing at least one audio/video data stream; an interface having a plurality of contacts including a power supply contact; and a voltage detector configured to measure a voltage on the power supply contact and to categorize the measured voltage as pertaining to one from a plurality of predetermined voltage ranges; wherein said security module is configured to function according to any one from a plurality of predetermined operation modes depending on a category of the measured voltage on the power supply contact following power-on, said operation mode including any communication protocol from a plurality of different communication protocols or any class from a plurality of classes of a communication protocol; and wherein the security module is configured to monitor the category of the measured voltage from the voltage detector following power-on and to switch to a different one from the plurality of operating modes in response to a change in the category.
 2. The security module according to claim 1, wherein the plurality of contacts are positioned in such a way as to be compatible with the International Standard ISO 7816 according to at least the physical characteristics described therein, said physical characteristics including at least the dimensions and locations of the contacts described therein.
 3. The security module according to claim 1, wherein at least one parameter characterising any of the plurality of operation modes is a frequency of operation, the frequency of operation of at least one of the operation modes being compatible with the International Standard ISO
 7816. 4. The security module according to claim 3, wherein the frequency of operation of at least one of said plurality of operation modes is higher than the frequency of operation of any one of the remaining operation modes from the plurality of operation modes.
 5. The security module according to claim 1, wherein at least one of the plurality of operation modes makes use of at least one from the plurality of contacts defined as RFU (Reserved for Future Use) according to the International Standard ISO
 7816. 6. The security module according to claim 1, further comprising a frequency divider to produce a communication frequency from a clock generator frequency, said communication frequency being lower than the clock generator frequency, said communication frequency being used to provide a clock signal for at least one of the predetermined operation modes, said clock signal determining the frequency of operation.
 7. The security module according to claim 1, further comprising a frequency multiplier to produce a communication frequency from a clock generator frequency, said communication frequency being higher than the clock generator frequency, said communication frequency being used to provide a clock signal for at least one of the predetermined operation modes, said clock signal determining, the frequency of operation.
 8. A method for processing an audio/video signal using a security module comprising a processor for processing the audio/video signal, an interface having a plurality of contacts including a power supply contact, and a voltage detector configured to measure a voltage on the power supply contact, said method comprising the following steps: powering the security module via the power supply contact; measuring the voltage on the power supply contact; determining a category to which the measured voltage pertains, said category being one from a plurality of predetermined categories; selecting an operation mode from a plurality of predetermined operation modes, said selection depending on the monitored category, said operation mode including any communication protocol from a plurality of different communication protocols or any class from a plurality of classes of a communication protocol; and operating the security module according to the selected operation mode.
 9. The method for processing an audio/video signal according to claim 8, wherein it further comprises monitoring the category of the measured voltage from the voltage detector and switching to a different one from the plurality of operation modes upon a change in the category of the measured voltage.
 10. The method for processing an audio/video signal according to claim 8, wherein said security module further comprises a clock divider to divide a clock signal from a clock generator, said clock signal having a first frequency, said clock divider providing a communication clock with a second frequency which is lower than the first frequency, either the clock signal or the communication clock being used to provide timing control for the selected operation mode depending on which operation mode is selected.
 11. The method for processing an audio/video signal according to claim 8, wherein said security module further comprises a clock multiplier to multiply a clock signal from a clock generator, said clock signal having a first frequency, said clock multiplier a communication clock with a second frequency which is higher than the first frequency, either the clock signal or the communication clock being used to provide timing control for the selected operation mode depending on which operation mode is selected.
 12. The method for processing an audio/video signal according to claim 8, wherein said security module further comprises a clock divider to divide a clock signal from a clock generator and a clock multiplier to multiply a clock signal from a clock generator, said clock signal having a first frequency, said clock divider providing a second communication clock with a second frequency which is lower than the first frequency, said clock multiplier providing a third communication clock with a third frequency which is higher than the first frequency, said second communication clock or said third communication clock being used to provide timing control for the selected operation mode depending on which operation mode is selected.
 13. A decoder for decoding an audio/video data stream, said decoder comprising: a clock generator to generate a first clock having a first clock frequency; a security module interface, said security module interface comprising a least a power terminal; and a power supply connected to supply power to the power terminal; wherein the decoder is configured to set a voltage supplied to the power terminal to correspond to one from as plurality of predetermined voltage ranges, each of the predetermined voltage ranges corresponding to a communication protocol from a plurality of different communication protocols or a class from a plurality of classes of a communication protocols. 